Cannabis plants go through two stages of
life, the "vegetative" stage and the "flowering stage."

They first go through the
vegetative life stage, which you can sort of consider its
"childhood" since the plant is only focusing on growing bigger and
taller, and gender doesn't matter. At the beginning of this
stage you usually can't tell what the plant's gender is.

However, once the plant
is about 6 weeks old, it will usually show signs of "pre-flowers" which
will alert you to the gender before the beginning of the flowering
stage.

Next, cannabis plants switch to the flowering
stage which means they stop growing bigger and
taller, and instead spead all their effort growing flowers
(the buds we want are flowers!). The flowering stage is like the
"adult" stage of a cannabis plant since at this point it's only
interested in adult stuff like growing their male and female parts,
then pollinating :) In the flowering stage, plants
start growing buds or pollen sacs in earnest. The
buds we want are female flowers, so growers generally only want to grow
female plants.

Growers Want Female
Cannabis Plants - These Produce Bud

Regular Marijuana plants reveal
their gender in two situations:

After spending a long time in the
vegetative stage - some strains/plants will show preflowers (pistils
for girls and “balls” for boys) during the vegetative stage if they
grow old enough, even when they are constantly kept under a vegetative
light schedule. For example, clones can come from plants that are
several years old, so you’ll see a lot of clones have female pistils
showing, yet will not continue to flower any more than that until after
they’ve been switched to a Flowering (12-12) light schedule

Otherwise, all remaining plants will
reveal their gender in the first 1-3 weeks after lights are switched to
12-12, and plants enter the flowering stage of life.

When your cannabis plant is
about to reveal it's gender, what you're looking for is cannabis
"pre-flowers." These usually show up when the plant is around
6 weeks old from seed, but they always appear once the plant is changed
over to the flowering stage.

Male and female
pre-flowers look different from each other (though it can be easy to
confuse them at first). Sometimes it's hard to tell which is
which at first, and in that case you'll just have to wait until they
develop a few more flowers and it becomes more obvious.

Diagram Showing What Pre-Flowers
Look Like
Male pre-flowers on left - Female pre-flowers on right

Female marijuana plants take a bit longer than males to show
their first signs after being changed over to flowering.

Female marijuana plants start showing one or two wispy white
white hairs where their buds are going to start forming.

They usually first show up where the main stem connects to the
individual nodes or 'branches'.

If a female plant is kept in the vegetative stage long enough
(the length of time varies depending on the strain and conditions),
then she will start showing the first sign of female hairs even before
you move the plant into the flowering stage by changing the light
schedule.

If you see wispy white hairs appearing on your plant like the
ones pictured below, then you know you have a female plant.

Click on thumbnails for
larger picture

In this pic, you can see white
pistils emerging from the calyxes. Female pistils are white and wispy,
never green.

This pre-flower doesn't have a pistil
sticking out at first, but the shape helps tell you it's a female
plant. If you're not sure about gender after spotting a pre-flower,
it's a good idea to wait and see for a little while, just to see if a
white hair appears (which means it's definitely a girl)

Adult
Female Cannabis Plant Pictures

Those buds turn into this!

Male
Marijuana Plant Pictures

Male plants have grape-like balls which form and fill with
pollen. The balls will first show up a week or two after changing the
plants over to the flowering stage. If the male is allowed to continue
growing, eventually these pollen sacs will burst open and spill pollen
everywhere.

A small male pre-flower -
this is what male plants look like when they first reveal their gender

These male pre-flowers are basically
immature pollen sacs. When the plant starts flowering, they will grow
and turn into bunches that almost look like grapes.

Sometimes it takes a
day or two for a female pre-flower to release her first pistil, and the
female calyx can look like the beginning of a pollen sac. Generally the
more "pointy" ones tend to be female, but sometimes you have to wait
and see a few more flowers to know for sure.

Life Stages:
What Do I Need to Know About the Vegetative & Flowering Stages?

That means you use an electricity timer to automatically
shine your grow lights for 12 hours a day, with 12 hours of
uninterrupted TOTAL darkness during the plant's "night period."

Marijuana plants should reveal the first
signs of their gender within 2-3 weeks after being changed to 12-12.

How
Light Schedules Affect Marijuana Life Stages

Marijuana plants have an internal process
where they can detect how long they receive uninterrupted darkness each
day.

In the wild, as the days get shorter and
nights get longer, the marijuana plant "realizes" that winter is coming
and will start budding/flowering as it approaches the end of it's life
cycle.

When growing marijuana outdoors, a grower
doesn't need to do anything to induce flowering because the sun will
take care of things on its own. All you need to do is make sure your
plant isn't directly under a street light or other light source, so
that the plant receives complete darkness at night.

However,
when growing marijuana indoors, a marijuana gardener will have to
"fool" their plants into thinking winter is coming to induce flowering
and kickstart the creation of buds.

This is done by changing the plant's light
schedule to 12-12, where the weed plants gets 12 hours of light a day
and 12 hours of total darkness.

It's easier to ensure the plant gets the 12
full hours of darkness each night when the start and end time for your
lights to turn on and off is exactly the same each day. This is why
most growers end up getting a timer to
turn their lights on and off automatically.

I tend to set my timer in flowering to shine
line from 7pm-7am. This gives me time to check on my plants at night
when the lights first come on, and I can also check them quickly in the
morning before I go to work. It also keeps things cooler since the
lights are on at night. Some people (like myself) also get discounts on
electricity that's used at night.

But ANY 12 hour dark period will work, as
long as you prevent your plant from getting light leaks during their
"night."

In fact, with marijuana plants, the
length of night period, not the length of day period,
seems to make the biggest difference. This makes sense if you consider
that in the wild, a stormy or cloudy day could shorten the light period
a plant receives, but few things in the wild will interrupt the
darkness of night.

This has been experimentally verified by some
out-of-the-box thinkers. They gave marijuana plants different amounts
of light and dark, then watched what happened.

What they found is that a marijuana plant
will stay flowering as long as she gets 12+ hours of darkness on a
regular basis. The length of day period didn't seem to matter at all.
In fact, you could give plants 12 hours of dark followed by 24 hours of
light, on a regular basis, and plants would continue to flower as long
as their darkness was uninterrupted for 12 hours at a time.

Only a female marijuana plant makes
flowers/buds that contain a usable amount of THC. Male marijuana plants
only make pollen sacs that they use to fertilize the females. Most
growers will throw away any male plants that they encounter to keep
them from fertilizing the female plants. If your female plants do get
fertilized, they will use all their energy to produce seeds instead of
making buds. This is good if you want seeds, but you will run into the
same problem since half of the seeds will also be male.

If you would like to start a breeding program
to make your own hybrids, I recommend using a method that creates
all-female (feminized) seeds so that you don't waste time having to
identify and throw out male plants.

Getting
clones of female marijuana plants or buying feminized seeds online from
a seed
bank are other ways you can ensure that all your marijuana
plants are female.

If you don't have a choice of seeds, and some
of your seeds may be male (like if you just found seeds) than you will
want to get your plants to reveal their gender right away so you don't
have to waste time and energy on male plants.

For most marijuana strains, the male plants
don't produce usable amounts of THC, so most growers toss them on
sight. Unfortunately, 50% of all regular seeds will become male plants.

These male plants can also impregnate your
female plants, which causes them not to produce as many buds, so unless
you're breeding, destroy male plants as soon as you notice them growing
grape-like balls where their buds would normally be.

A vigilant grower can carefully watch their
plants and remove males when they develop the first signs of pollen
sacs.

How to identify female plants if
starting out with regular bagseed?

You don't have to wait for the flowering
stage! Below we'll share two tactics growers use to identify
gender in the vegetative stage.

Tactic
1: Preflowers let you identify plants in week 3-6 from seed

Pre-Flowers reveal
the gender of your plant by around week 6 from seed, and as early as 3
weeks from seed for some plants.

In this area you'll find pre-flowers
nestled where the "joints" of the plant are.

The following method can help you identify
gender for plants that are taking a while to show their pre-flowers.

If you're just growing 1, 2, or 3 plants, it
can be heartbreaking to find out all your plants are male, and you need
to start over in order to make buds.

When marijuana plants are seedlings (or when
they're just seeds), there's no way to tell which plants are male and
which plants are female.

You have to "wait and see." Male
marijuana plants develop pollen sacs (look like little balls or
nuts). Female marijuana plants start growing white hairs that
develop into the marijuana buds (sensimilla) that
contain THC and other cannabinoids. Lots
of pictures of male and female parts above.

However, you may want to be more proactive
and get rid of the male plants before they enter the flowering stage so
you don't have to waste the time and energy in caring for plants that
you will eventually get rid of. If so, then you can use to following
technique to identify and remove all the males from your grow.

How to Determine Sex of a
Marijuana Plant

You can wait until your plants naturally
show the first signs of their gender and then remove all the males, but
that means you have to watch the plants closely. You also will waste
time and energy growing plants only to find out that some or all are
male and have to throw them away. If you want to be more proactive and
get rid of all male plants right away, then use this technique.

Label both the clone and the mother plant
so you know which clone came from which corresponding mother. If you
don't label them clearly, then all your effort will go to waste!

Once the clones have established roots,
change just the clones into flowering mode by providing them with a
light schedule of 12 hours on, 12 hours off

The clones should start revealing their
gender in a week or two. Males will start developing balls and females
will start developing white hairs. Click on the pictures below to see
some examples of male and female plants.

Once you have determined the gender of
your clones, you should make sure you throw away any corresponding male
plants.